1. Field of the Invention
The present invention relates generally to power plants and to fluid reaction surfaces, and more specifically to hot gas flow turbine components with internal cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Gas turbine engines—either aero engines used in aircraft or industrial gas turbines used to produce electric power—make use of a high temperature turbine to convert a hot gas flow into mechanical work by rotatably driving the turbine shaft. The efficiency of a gas turbine engine can be increased by pass into the turbine a higher temperature flow, since the energy content of the flow is proportional to the temperature of the flow. However, the hot gas flow temperature is limited to the material properties of the components of the turbine such as the rotor blades and the stationary vanes or nozzles.
In order to allow for a higher gas flow temperature using the same materials, internal air cooling of turbine airfoils such as blades and vanes has been used. Since the cooling air used to pass through the airfoils is usually drawn off from the compressor (known as bleed off air), the efficiency of the engine can also be increased my using a minimal amount of bleed off air. Therefore, the use of the cooling air passing through the internal passages of the turbine airfoils is also a key design feature of engineers such that the cooling efficiency of the passing air can be maximized.
Turbine airfoils have complex internal cooling air passages in order to improve heat transfer from the airfoil to the cooling air. Because of this complexity, some parts of the airfoil may be cooled too much while other parts may not be cooled enough. Also, centrifugal forces (in rotor blades) and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending upon their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade.
Other components in the gas turbine engine are exposed to the hot gas flow besides the turbine airfoil. The combustor includes walls that are sometimes cooled by passing a cooling air through passages formed within the walls. The ideas of the present invention could also be used to promote the heat transfer effect from the component to the cooling air passing through the component.
One prior art invention, U.S. Pat. No. 6,808,367 B1 issued to Liang on Oct. 26, 2004 entitled COOLING SYSTEM FOR A TURBINE BLADE HAVING A DOUBLE OUTER WALL discloses an airfoil formed by an inner wall and an outer wall, in which a plurality of pedestals (#46 in this patent) extend between the inner wall and the outer wall and a plurality of protrusions. (#54 in this patent) positioned between the pedestals in order to create a spiral flow of the cooling air through the cooling passage in the airfoil. The spiral flow path improves the heat transfer from the walls of the airfoil to the cooling air without increase the cooling air flow rate. In this Liang patent, the protrusions can extend from the inner wall, from the outer wall, or from both the inner and the outer walls.
U.S. Pat. No. 6,984,102 B2 issued to Bunker et al on Jan. 10, 2006 entitled HOT GAS PATH COMPONENT WITH MESH AND TURBULATED COOLING discloses an improvement from the above Liang patent. Pins (#18 in this patent) extend between the inner wall and the outer wall like in the Liang patent above, but include turbulators plates (#36 in this patent) that extend from pin to pin, and also extend toward the opposing wall. The pins are arranged along a transverse direction of the cooling flow, or angled with respect to the transverse direction, or with alternating segmented turbulators. The Bunker et al patent arranges the pins to form a mesh arrangement with turbulators on at least one of the walls in order to provide an enhanced cooling effectiveness for hot gas components having thin airfoil walls.
It is an object of the present invention to improve the efficiency of a gas turbine engine. It is another object of the present invention to improve the heat transfer from the hot airfoil surface to the cooling air passing through the airfoil. It is another object of the present invention to increase the turbulence of the cooling air flow passing through an arrangement like the Liang patent and the Bunker patent described above.